In the fabrication of semiconductor devices, various processing steps, i.e., as many as several hundred, are necessary to process a bare silicon wafer to a completed semiconductor chip. One of the processing steps which must be repeated many times to define features or circuits on the wafer surface throughout the total fabrication is photolithography. In photolithography, a photoresist material in the form of a liquid is first dispensed uniformly on the surface of a wafer and then dried. The photoresist material is then exposed by one of several imaging techniques to reproduce a pattern of circuits. After the pattern of circuits is exposed in the imaging process, i.e., possibly in a stepper machine, a developer liquid is dispensed on the photoresist layer to develop the image. These processes, i.e., the photoresist coating process, the exposure or imaging process and the developer coating process can be carried out in either an off-line method or an in-line method. In the off-line method, the photoresist liquid is coated uniformly on the surface of a wafer in a coating machine and then dried, the wafer is then transported by an operator to a separate machine for the next step imaging and developer coating process. In more recently developed equipment, an in-line method is frequently used in which the photoresist coating process, the exposure or imaging process by a stepper and the developer coating process are performed in the same process machine at different stations. The wafer is transferred automatically between the stations without the attendance of an operator. The in-line process is therefore more economical to perform and higher quality product can be produced with reduced contamination problems.
In either the in-line process or the off-line process for photolithography, the step of applying a developer coating on the surface of a wafer is carried out by a liquid dispensing nozzle. The nozzle is normally constructed of stainless steel which has a multiplicity of capillary openings provided on a dispensing surface of the nozzle. A liquid flow is fed into the nozzle head through an inlet opening and transported to the multiplicity of capillary openings through numerous passages. A typical liquid dispensing system for a developer liquid is shown in FIG. 1.
FIG. 1 shows a conventional developer liquid dispensing system 10 consisting of a dispensing nozzle head 12 which is mounted on a liquid dispense arm 16. The liquid dispense arm moves in a horizontal position, i.e., to the left for dispensing a developer liquid on the surface of a wafer 20 mounted on a wafer chuck (not shown) and a rotating shaft 22, or to the right to a nozzle bath 30 for cleaning. The conduits 18, 24 and 26 are used to convey to the nozzle head 12 the developer liquid, and to vent the nozzle head 12. The nozzle head 12 is shown in a perspective view in FIG. 2 showing the multiplicity of capillary openings 14.
In a conventional method for operating the liquid dispensing nozzle head 12, during each dispense cycle the dispensing arm 16 moves to the left and then lowers itself onto the surface of wafer 20. To avoid the generation of air bubbles in the developer liquid dispensed, the liquid dispensing nozzle head 12 is positioned very close to the surface of the wafer 20. For instance, a distance of approximately 1.5 mm is normally maintained so that the developer liquid can be dispensed on the wafer surface without a long travel distance. At such a close proximity from the wafer surface, it is inevitable that some developer liquid sticks to the nozzle face 36 (shown in FIG. 2). During each liquid dispensing action the dispensing arm moves to the left and dispenses a developer liquid on the wafer supported by a wafer chuck rotated by shaft 22 at a predetermined speed. The dispensing arm 16 then moves to the right and to a position over a nozzle path 30 and lowers itself into the bath. After dipping the nozzle head 12 into the bath 30 which contains a suitable cleaning solvent for a predetermined amount of time, an inert gas is used to blow the channel openings in the nozzle head through the capillary openings 14 in an attempt to clean out the fluid passages.
The conventional cleaning method and the apparatus used for cleaning are not adequate for a thorough cleaning of the nozzle head 12. One reason for this inadequacy is that, due to the close proximity between the nozzle face 36 and the wafer surface, the developer liquid stuck on the nozzle face 36 crystalizes into solid particles after a few dispensing operations have been conducted. The crystalized developer material on the nozzle face 36 thus becomes a potential source of particle contamination on the wafer surface. The particle contamination by the crystalized developer material causes serious quality problems for any IC devices fabricated on the wafer.
It is therefore an object of the present invention to provide an apparatus for cleaning a liquid dispensing nozzle utilized in a semiconductor processing machine that does not have the drawbacks and shortcomings of the conventional apparatus used for cleaning such nozzles.
It is another object of the present invention to provide an apparatus that can be used effectively in cleaning a liquid dispensing nozzle used in a semiconductor processing machine that is equipped with a pressurized liquid bath into which a liquid dispensing nozzle can be immersed.
It is a further object of the present invention to provide an apparatus for cleaning a liquid dispensing nozzle used in a semiconductor processing machine that is equipped with a cleaning solvent buffer tank capable of feeding a cleaning solvent under pressure to a cleaning solvent reservoir tank into which a dispensing nozzle may be immersed.
It is another further object of the present invention to provide an apparatus for cleaning a liquid dispensing nozzle used in a semiconductor processing machine that is equipped with a cleaning solvent reservoir tank which has a level sensor and a drain passage for controlling the level of the cleaning solvent in the tank.
It is still another object of the present invention to provide a method for effectively cleaning a liquid dispensing nozzle utilized in a semiconductor processing machine that can be carried out by first rinsing the dispensing nozzle in a cleaning solvent and then purging the nozzle with a processing fluid to be dispensed.
It is yet another object of the present invention to provide a method for cleaning a liquid dispensing nozzle utilized in a semiconductor processing machine that is carried out by first pressurizing a cleaning solvent reservoir tank such that cleaning solvent enters capillary openings in the nozzle to throughly clean all fluid passages.
It is still another further object of the present invention to provide a method for cleaning a liquid dispensing nozzle utilized in a semiconductor processing machine in which the nozzle is blown out after a cleaning process such that no residual cleaning solvent may be syphoned back into a processing liquid reservoir and diluting the processing liquid.